Research on BHAST Test Method for Plastic Encapsulated Microcircuit

Compared to metal packaging and ceramic packaging, plastic encapsulated microcircuits (PEMs) have the advantages of light weight and low cost. However, due to their non-airtightness, they are prone to delamination, corrosion, and other failures in humid and hot environments. In engineering practice, the unbiased highly accelerated stress test (UHAST) without bias voltage is commonly used to evaluate the moisture and heat resistance of PEMs, but it cannot fully excite the potential defects of PEMs. Therefore, it is necessary to consider the biased highly accelerated stress test (BHAST) with bias voltage applied. In this paper, the BHAST test method for PEM was studied, and four different bias voltage application methods were set up. Four consecutive HAST tests were conducted, and failure analysis was conducted on the samples. It can be confirmed that the BHAST test mainly stimulated the corrosion failure of the aluminum solder pads in the bonding area of the PEMs. Comparing the failure situation of the samples, it was found that under the condition of voltage application method 4, the samples failed the fastest and the number of corroded bonding areas appeared the most. It can be concluded that a reasonable bias voltage application method can be summarized as follows: after supplying power to the power pins, apply bias voltage alternately to the IO pins as much as possible.